diff --git a/src/cookie-jar.mjs b/src/cookie-jar.mjs
index 88f4fbe..13912bc 100644
--- a/src/cookie-jar.mjs
+++ b/src/cookie-jar.mjs
@@ -1,7 +1,7 @@
-import { promises as fs } from "fs";
+import {promises as fs} from "fs";
 import url from "url";
 import Cookie from "./cookie.mjs";
-import { paramError, CookieParseError } from "./errors.mjs";
+import {paramError, CookieParseError} from "./errors.mjs";
 
 export default class CookieJar {
     constructor(file, flags = "rw", cookies) {
diff --git a/src/cookie.mjs b/src/cookie.mjs
index 9ba283a..7cacd37 100644
--- a/src/cookie.mjs
+++ b/src/cookie.mjs
@@ -1,5 +1,5 @@
 import url from "url";
-import { paramError, CookieParseError } from "./errors.mjs";
+import {paramError, CookieParseError} from "./errors.mjs";
 
 const validateHostname = (cookieHostname, requestHostname, subdomains) => {
     cookieHostname = cookieHostname.toLowerCase();
diff --git a/src/errors.mjs b/src/errors.mjs
index fd36d17..94a3e6a 100644
--- a/src/errors.mjs
+++ b/src/errors.mjs
@@ -6,7 +6,7 @@ export class CookieParseError extends Error {
 };
 
 export function paramError(position, paramName, functionName, validTypes) {
-    validTypes = [validTypes].flatMap(t => "\"" + t + "\"");
+    validTypes = [validTypes].flat().map(t => "\"" + t + "\"");
     validTypes = validTypes.slice(0, -1).join(", ") + (validTypes.length > 1 ? " or " : "") + validTypes.slice(-1);
     return new TypeError(`${position} parameter "${paramName}" passed to "${functionName}" is not of type ${validTypes}!`);
 };
diff --git a/src/index.mjs b/src/index.mjs
index 40db751..1bdc532 100644
--- a/src/index.mjs
+++ b/src/index.mjs
@@ -1,7 +1,7 @@
 import _fetch from "node-fetch";
 import CookieJar from "./cookie-jar.mjs";
 import Cookie from "./cookie.mjs";
-import { paramError, CookieParseError } from "./errors.mjs"
+import {paramError, CookieParseError} from "./errors.mjs"
 
 async function fetch(cookieJars, url, options) {
     let cookies = "";